No manufacturer will ever admit to this, but the same things happen to certain people with all types of smart watch or fitness tracker/watch. What do they all have in common? Heart rate monitors! Those strobing lights that constantly burn into the flesh (for some people) . It's too common a thing for it to be caused by anything else. I've never suffered from it, but my other half does. I'm assuming it's dependant on skin type/sensitivity, etc. Ultimate test would be to give that wrist a rest for a while, let it heal. Put the watch back on with the sensor turned off and see what happens.

i was on the chat today to support and all they have told me is to wash the strap and not wear it for days - excuse me ? why did we buy our watches = to wear - what a terrible answer to a common problem that we are all experiencing

That is very poor design and after care. I'm burnt on the edges of my wrist which looks like I've burnt it on hot surface its that bad. I would think if it was a reaction it wouldn't resemble a burn it would be a rash.

I had a problem after first buying the watch in September 2018. Burns on my wrists, from the strap.

After some dialogue with Samsung UK they agreed to cover the cost of a replacement leather strap. They didn't have any available in the Samsung Store at the time and so offered me a payment to cover the cost of a replacement strap. I purchased a steel one and a quality leather one from Amazon and have had no further problems.

It's impossible for the LEDs to deal damage, the light your skin experiences every day is much stronger. Rashes are common with rubber bands since they don't let your skin breath and don't let sweat out which irritates it. The plastic surrounding the sensor hast the same effect. In my experience, it always helps to change the band to leather or steel.